1. Field of the Invention
The present invention relates to a DDR type zeolite seed crystal, a production method thereof, and a production method of a DDR type zeolite membrane. More specifically, the present invention relates to a DDR type zeolite seed crystal capable of inhibiting generation of surplus DDR type zeolite crystals when the DDR type zeolite seed crystal is used as a seed crystal upon forming a DDR type zeolite membrane on the surface of the porous support, and to a method for manufacturing the DDR type zeolite seed crystal. In addition, the present invention relates to a method for manufacturing a DDR type zeolite membrane capable of inhibiting generation of surplus DDR type zeolite crystals.
2. Description of Related Art
Zeolite is used as a catalyst, a catalyst carrier, an adsorbent, and the like. In addition, a zeolite membrane formed on the surface of the porous support made of metal or ceramic utilizes a molecular sieve function of zeolite, and is becoming popular as a gas separation membrane or a pervaporation membrane.
As zeolite, there are many kinds such as LTA, MFI, MOR, AFI, FER, FAU, and DDR depending on their crystal structures. Of these, a DDR (Deca-Dodecasil 3R) type zeolite is a crystal having silica as the main component. Its pores are formed by a polyhedron including an oxygen eight-membered ring. Furthermore, it is known that the pore size of the oxygen eight-membered ring is 4.4×3.6 angstrom. These are described in “W. M. Meier, D. H. Olson, Ch. Baerlocher, Atlas of zeolite structure types, Elsevier (1996)”.
A DDR type zeolite has relatively small pore sizes among zeolites and may be usable suitably as a molecular sieve membrane for low molecular gas such as carbon dioxide (CO2), methane (CH4), and ethane (C2H6).
As such a method for forming a DDR type zeolite membrane on the surface of a porous support, first, DDR type zeolite crystals functioning as seed crystals are prepared (see, e.g., non-patent documents 1 to 3 and patent documents 1 and 2). Then, there is a method wherein the DDR type zeolite seed crystals are applied on the surface of the porous support in advance, and then subjected to hydrothermal synthesis in a raw material solution, to grow to form a membrane (see, e.g., Patent Documents 3 and 4).